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Notes:
a. The value of a quantity may be positive, negative or zero.
b. The value of a quantity m ay be expressed in more than one way.
c. The values of quantities of dimension one are generally expressed as pure numbers.
d. A quantity that cannot be expressed as a unit of measurement multiplied by a number may be
expressed by reference to a conventional reference scale or to a measurement procedure or to
both.
True value (of a quantity)
Value consistent with the definition of a given particular quantity.
Notes:
a. This is a value that would be obtained by a perfect measurement.
b. True values are by nature indeterminate.
c. The indefinite article “a,” rather than the definite article “the,” is used in conjunction with “true value”
because there may be many values consistent with the definition of a given particular quantity.
Conventional true value (of a quantity)
Value attributed to a particular quantity and accepted, sometimes by convention, as having an uncertainty
appropriate for a given purpose.
Notes:
a. “Conventional true value” is sometimes called assigned value, best estimate of the value, conventional
value or reference value.
b. Frequently, a number of results of measurements of a quantity are used to establish a conventional
true value.
Measurement
Set of operations having the object of determining a value of a quantity.
Note:
a. The operations may be performed automatically.
Principle of measurement
Scientific basis of measurement
Method of measurement
Logical sequence of operations, described generically, used in the performance of measurements.
Note:
a. Methods of measurement may be qualified in various ways such as:
i. Substitution method
ii. Differential method
iii. Null method
Measurement procedure
Set of operations that are described specifically and are used in the performance of particular
measurements according to a given method.
Note:
a. A measurement procedure is usually recorded in a document that is sometimes itself called a
“measurement procedure” (or a measurement method) and is usually in sufficient detail to enable
an operator to carry out a measurement without additional information.
Measurand
Particular quantity subject to measurement
Note:
a. The specification of a measurand may require statements about quantities such as time, temperature
and pressure.
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